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New report concludes: Motorways are more annoying than urban roads

DELTA has assisted the Danish Road Directorate in a socio-acoustic survey. The results from the survey were quite surprising and so interesting that we would like to share them with our DELTA Agenda readers.

It is well-known fact that the same noise levels from different noise sources (e.g. roads, railways, aircrafts, and wind turbines) give rise to different degrees of noise annoyance – but, is one type of road more annoying than another? This was examined in a newly issued noise annoyance survey conducted by DELTA for the Danish Road Directorate. The results were quite surprising and have attracted attention from road authorities in other European countries.

Jakob Fryd, Project Manager at the Danish Road Directorate, says about the survey: “From our corporation in two earlier projects we knew that consultancy from DELTA would be a valuable contribution to the planning and analysis of this survey. We have really obtained new knowledge from this project, which has also attracted attention abroad.”

Thoroughly selected roads, areas, and respondents

The main purpose of the survey was to study people’s experience of the noise annoyance from motorways and urban roads. Thus, the survey was performed along motorways and urban roads in major cities in Denmark. Figure 1 gives an overview of motorway sections and cities included in the study.

Figure 1 – Motorway sections and cities included in the study.

Nearly 7,000 respondents were carefully selected for the survey. It was especially important that the respondents lived in areas where the primary source of road traffic noise was motorways and urban roads, respectively. Furthermore, it was important that the respondents, and the environments in which they live, roughly were representative of people who live along motorways and urban roads in Denmark.

Surprising results

The answers from the approximately 7,000 respondents were closely analysed together with the noise levels at the most exposed facade.

Dose-response relationship (i.e. the relationship between the respondents’ noise annoyance and the noise impact) between noise and annoyance, was established for ‘Highly Annoyed’, ‘Annoyed’, and ‘Little Annoyed’, respectively. Figure 2 shows the percentage of ‘Highly Annoyed’.

As illustrated in figure 2, the results show that people who live along motorways are significantly more annoyed by road traffic noise compared to people who live along urban roads – when they are exposed to the same noise exposure. In fact, at a noise level of Lden = 65 dB (at the most expose façade) approximately 2.5 times as many people are ‘Highly Annoyed’ along the motorways compared to the urban roads. Traditionally, it has been assumed that the two curves would be nearly identical. However, the survey results indicate that more people than previously assumed are annoyed by the noise from motorways.

The results can also be seen in another way: 20 % of respondents living along urban roads are ‘Highly Annoyed’ at a level of Lden = 68 dB, while 20 % of respondents living along motorways are ‘Highly Annoyed’ at Lden = 57 dB. This corresponds to a level difference of more than 10 dB for the same degree of annoyance for the two road types!

The surprising results indicate a need to consider noise from motorways separately from noise from other roads. But is this only a Danish phenomenon?

Motorway noise at a European level

The Danish dose-response curves (see figure 2) were compared to the curves for road traffic noise given in the EU-position paper Position paper on Dose-response relationships between transportation noise and annoyance”. ISBN 92-894-3894-0, European Communities, 2002.. On the basis of the study, it can be concluded that people who live along motorways in Denmark are significantly more annoyed than shown by the European noise annoyance curves, whereas the annoyance for people who live along urban roads is in line with the general European curves. The results indicate that the problem may prevail in other European countries as well, i.e. people living close the motorways around Europe are also more annoyed by the noise than previously assumed.

It was not the purpose of the investigation to specify actions or assess the consequences of the fact that the reported noise annoyance is significantly higher than assumed earlier. However, the results give rise to considerations about how it can be taken into account in the future that road traffic noise from motorways and road traffic noise from urban roads are perceived very differently.